You can simplify that wantarray call by adding a return in front and then letting the ternary operators do the rest like so:

return wantarray ? @file : join '', @file;
[download]

And here is my slightly changed version of your code.

#!/usr/bin/perl
sub io
{
# usage:
# @array  = io('read',$file)
# $string = io('read',$file)
# io('write',$file,\$string)
# io('write',$file,\@array)

my($bit,$file,$data) = @_;

if($bit eq 'read'){
    open IO,"< $file" or die "Cannot open $file for input: $!\n";
    my @file = <IO>;
    close IO;
    return wantarray ? @file :  join '', @file;
    }
if($bit eq 'write'){
    open  IO,"> $file" or die "Cannot open $file for output: $!\n";
    print IO  ref $data eq 'ARRAY' ? @$data : ref $data eq "SCALAR"? $
+$data : '';
    close IO;
    }
}
$string = "YO!";
io('write','file.txt',\$string);
[download]

This way everything is passed as references and it deletes an extra line of code. :)

$_.=($=+(6<<1));print(chr(my$a=$_));$^H=$_+$_;$_=$^H;
print chr($_-39); # Easy but its ok.
[download]

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